In this paper, the verticalseismic effects on tunnels are studied based on a classic mass–damper–spring model. An analyticaldiscrete modelof urban underground tunnels subjected to verticalearthquake excitations is p...In this paper, the verticalseismic effects on tunnels are studied based on a classic mass–damper–spring model. An analyticaldiscrete modelof urban underground tunnels subjected to verticalearthquake excitations is proposed by considering the first verticalvibration mode. Taking a light railproject in Tianjin as an example, this study uses the proposed discrete modelto analyze the displacements of tunneland soilunder verticalearthquake excitations. The soildisplacement responses at different tunnellocations are analyzed with linear random vibration theory.The computationalcost is greatly reduced using the proposed model. It can be seen that different from the case of horizontalearthquakes, the displacement responses under verticalearthquake excitations keep growing after seismic acceleration reaches its peak for a short duration, and then,they begin to decay. The soils at different positions around the tunnels have large relative displacement under verticalearthquake excitations. Moreover, a finite-element modelis also established for displacement responses using ABAQUS.The comparison with the results of the finite-element modelshows that the results of the proposed discrete modelare available.展开更多
Estimating safety effectiveness of roadway improvements and countermeasures,using cross-sectional models,generally requires large amounts of data such as road geometric and traffic-related characteristics at road segm...Estimating safety effectiveness of roadway improvements and countermeasures,using cross-sectional models,generally requires large amounts of data such as road geometric and traffic-related characteristics at road segment levels.These models do not consider all confounding crash contributory factors such as driving culture and environmental conditions at the segment level due to a lack of readily available data.This may result in inaccurate models representing actual conditions at road segment levels,followed by erroneous estimations of safety effectiveness.To minimize the effect of not including such variables,this study develops a new methodology to estimate safety effectiveness of roadway countermeasures,based on generalized linear mixed models,assuming zeroinflated Poisson distribution for the response,and adjusting for spatial autocorrelation using the spatial random effect.The Bayesian approach,with Integrated Nested Laplace Approximation,was used to make inference on this model with computational efficiency.Results showed that incorporating a spatial random effect into the models provided better model fit than non-spatial models;hence,estimated safety effectiveness based on such models is more accurate.The proposed approach is a methodological advancement in traffic safety,which allows evaluation of safety effectiveness or roadway improvements when data are not readily available.展开更多
为了研究频域法中的应力幅值概率密度函数(Probability Density Function,PDF)模型在随机振动疲劳寿命评估过程中的适用性,首先介绍常用的5种频域法模型,接着设置由不同谱宽系数、中心频率和功率谱密度(Power Spectral Density,PSD)谱...为了研究频域法中的应力幅值概率密度函数(Probability Density Function,PDF)模型在随机振动疲劳寿命评估过程中的适用性,首先介绍常用的5种频域法模型,接着设置由不同谱宽系数、中心频率和功率谱密度(Power Spectral Density,PSD)谱值组合的限带白噪声应力功率谱。在此基础上利用傅里叶逆变换得到对应的时域信号,并将频域法模型计算得到的应力幅值概率密度函数与模拟的时域信号经过雨流循环计数得到的结果进行对比,评估各种频域模型的适用性和精度。结果表明,在整个带宽范围内,ZhaoBaker模型和Dirlik模型都有较高的准确性和适用性,Weibull模型在模拟小谱宽系数(ε<0.15)的单峰谱和谱宽系数大于0.6的宽带PSD时拥有不错的精度;频域模型的精度误差都随中心频率和谱值的增加有不同程度的下降。展开更多
基金supported by the National Natural Science Foundation of China (No. 51478311)the Natural Science Foundation of Tianjin, China (No. 14JCQNJC07400)
文摘In this paper, the verticalseismic effects on tunnels are studied based on a classic mass–damper–spring model. An analyticaldiscrete modelof urban underground tunnels subjected to verticalearthquake excitations is proposed by considering the first verticalvibration mode. Taking a light railproject in Tianjin as an example, this study uses the proposed discrete modelto analyze the displacements of tunneland soilunder verticalearthquake excitations. The soildisplacement responses at different tunnellocations are analyzed with linear random vibration theory.The computationalcost is greatly reduced using the proposed model. It can be seen that different from the case of horizontalearthquakes, the displacement responses under verticalearthquake excitations keep growing after seismic acceleration reaches its peak for a short duration, and then,they begin to decay. The soils at different positions around the tunnels have large relative displacement under verticalearthquake excitations. Moreover, a finite-element modelis also established for displacement responses using ABAQUS.The comparison with the results of the finite-element modelshows that the results of the proposed discrete modelare available.
文摘Estimating safety effectiveness of roadway improvements and countermeasures,using cross-sectional models,generally requires large amounts of data such as road geometric and traffic-related characteristics at road segment levels.These models do not consider all confounding crash contributory factors such as driving culture and environmental conditions at the segment level due to a lack of readily available data.This may result in inaccurate models representing actual conditions at road segment levels,followed by erroneous estimations of safety effectiveness.To minimize the effect of not including such variables,this study develops a new methodology to estimate safety effectiveness of roadway countermeasures,based on generalized linear mixed models,assuming zeroinflated Poisson distribution for the response,and adjusting for spatial autocorrelation using the spatial random effect.The Bayesian approach,with Integrated Nested Laplace Approximation,was used to make inference on this model with computational efficiency.Results showed that incorporating a spatial random effect into the models provided better model fit than non-spatial models;hence,estimated safety effectiveness based on such models is more accurate.The proposed approach is a methodological advancement in traffic safety,which allows evaluation of safety effectiveness or roadway improvements when data are not readily available.
文摘为了研究频域法中的应力幅值概率密度函数(Probability Density Function,PDF)模型在随机振动疲劳寿命评估过程中的适用性,首先介绍常用的5种频域法模型,接着设置由不同谱宽系数、中心频率和功率谱密度(Power Spectral Density,PSD)谱值组合的限带白噪声应力功率谱。在此基础上利用傅里叶逆变换得到对应的时域信号,并将频域法模型计算得到的应力幅值概率密度函数与模拟的时域信号经过雨流循环计数得到的结果进行对比,评估各种频域模型的适用性和精度。结果表明,在整个带宽范围内,ZhaoBaker模型和Dirlik模型都有较高的准确性和适用性,Weibull模型在模拟小谱宽系数(ε<0.15)的单峰谱和谱宽系数大于0.6的宽带PSD时拥有不错的精度;频域模型的精度误差都随中心频率和谱值的增加有不同程度的下降。